1. Field of the Invention
The present invention relates to a keyboard circuit, and more particularly, to a keyboard circuit using conduits within a bus for air flow.
2. Description of the Prior Art
Please refer to FIG. 1 and FIG. 2. FIG. 1 is an exploded diagram of a prior art circuit board 10 for a keyboard 12, and FIG. 2 is a cross-sectional view of the circuit board 10. The circuit board 10 for the keyboard 12 is used to generate key signals. The keyboard 12 includes a base 14 and a plurality of key structures 16. The circuit board 10, disposed between the base 14 and the key structures 16, includes a thin film switching circuit 18 for generating key signals. The thin film switching circuit 18 includes an upper circuit layer 22 and a lower circuit layer 24.
As shown in FIG. 2, the upper circuit layer 22 includes a plurality of upper joints 26 corresponding to a plurality of lower joints 28 of the lower circuit layer 24. The key structures 16 are disposed over all sets of the upper joints 26 and the lower joints 28, and are movable in an upward and downward manner. Thus, the upper joints 26 are capable of being pressed down by the key structures 16 to cause the upper joints 26 to contact their respective lower joint 28 to generate corresponding key signals. An air-filled space 30 is between the upper joints 26 and the lower joints 28. When the key structures 16 are pushed downward, the upper joints 26 descends and contacts the lower joints 28; the upper joints 26 are designed to maintain or return to the original positions when the key structures 16 are not pressed or released.
Generally, there are two ways of designing the air-filled space 30. The first method is to isolate the air-filled space 30 to prevent dust and moisture from entering the air-filled space 30. This prolongs the life of the circuit board 10, but the upper joints 26 may become hard to be pressed down by the key structures 16 or to revert to the original positions when the outside atmosphere pressure or temperature varies. The user, thus, may felt inconvenient. Moreover, the circuit board 10 may generate incorrect key signals. The other method is to let the air-filled space communicated with the atmosphere to equalize internal and external pressures. This, however, leaves the circuit board 10 open to the atmosphere and cannot stop effectively the entering of external dust and moisture.
Please refer to FIG. 3. FIG. 3 is a schematic diagram of another prior art circuit board 32 designed to overcome the aforementioned problems. As shown in FIG. 3, a plurality of air passageways 33 are connected to a restrictive air passageway 34 that has a superior blocking effect than a device with air passageways 33 that are directly open to the outside.
Both the air passageways 33 and the restrictive air passageway 34 have openings on the thin film switching circuit 18, and so dust and moisture is able to enter the air-filled spaces 30. For example, if a user spills hot liquid on the thin film switching circuit 18, the air within the air-filled space 30 expands from the heat, leaving the air-filled spaces 30, and returns when the liquid cools down. Therefore, the liquid may be sucked through the restrictive air passageway 34 and the air passageways 33 into the air-filled spaces 30 when the liquid cools down. Therefore, the circuit boards 10 and 32 do not always satisfy the user""s wants.
It is therefore an objective of the present invention to provide a circuit board for a keyboard that not only adjusts the air pressure of the air-filled spaces within the keyboard, but also prevents dust and moisture from entering the air-filled spaces.
In accordance with the claimed invention, a thin film circuit includes a thin film switching circuit with an upper circuit layer including at least one upper joint, and a lower circuit layer with at least one lower joint corresponding to the upper joint. The lower circuit layer is set under the upper layer, and an air-filled space is disposed between the upper joint and the lower joint. The thin film switching circuit further includes at least one first air conduit set between the upper circuit layer and the lower circuit layer that is connected to the air-filled space. At least one bus structure is connected to the thin film switching circuit and extends out of the thin film switching circuit to transmit electrical signals from the thin film switching circuit. The bus structure includes at least one second air conduit. One end of the second air conduit is connected to the ambient atmosphere. The other end of the second air conduit is connected to the first air conduit so that the air in the air-filled space can flow in and out to the ambient atmosphere through the first air conduit and the second air conduit.
It is an advantage of the present invention that because the air in the air-filled spaces is able to flow in and out to the ambient atmosphere through the first air conduit and the second air conduit, the keyboard circuit is able to adjust pressure according to variations of the ambient atmosphere while preventing contaminants, such as dust or moisture, from entering the keyboard circuit.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.